The present invention relates to an image format converting method and apparatus, and more particularly, to a method and apparatus for enlarging and reducing an image.
In digital television systems, the size of an image to be displayed is not fixed. Specifically, in the case of high-definition television, the size of a displayed image varies greatly. However, general purpose image displays are designed to display an image with a predetermined resolution. Therefore, a need has developed for devices that convert various resolutions of input images into the resolution of the corresponding display. These devices are called xe2x80x9cimage format converterxe2x80x9d.
Also today, computer systems, as one type of image display apparatuses, further include hardware accelerators on graphics cards, for enlarging and reducing an image. Methods are also required for simply and effectively enlarging and reducing images.
As a result, various algorithms for enlarging and reducing a digital image have been suggested. These include zero-order interpolation, bi-linear interpolation, finite impulse response (FIR) filtering interpolation, etc. In addition, an algorithm for enlarging and reducing an image by controlling discrete cosine transform (DCT) coefficients in the frequency domain has been suggested.
These algorithms all have disadvantages. The DCT algorithm has a limited enlargement or reduction ratio, and is more complicated than the other algorithms. The zero-order interpolation is the simplest algorithm, however, its image quality deteriorates because the image signal is displayed only as values of the adjacent pixels. With bi-linear interpolation, an enlarged image is not distinct due to a low-pass filtering effect, and aliasing occurs when the image is reduced. Finally, the FIR filtering method provides an excellent image even when the image is enlarged or reduced, however, it requires a significant amount of calculation and restricts the transform of coefficients based on the enlargement or reduction ratio.
To solve the problems described above, an objective of the present invention is to provide an image format converter for enlarging and reducing an image in real-time with a simple structure that provides excellent image quality.
Another objective of the present invention is to provide an image format converting method for enlarging and reducing an image in real-time that provides excellent image quality.
To achieve the first objective, an apparatus for converting the resolution of an input image to enlarge and reduce the input image, has been designed that comprises a pre-filter and a format converter. The pre-filter outputs a pre-filtered image signal. The format converter performs a bi-linear interpolation on the pre-filtered image signal, according to a predetermined aspect ratio, and outputs a format-converted signal.
To achieve the second objective, a method for converting the resolution of an input image to enlarge and reduce the input image has been formulated that comprises the steps of: (a) pre-filtering the input image to output a pre-filtered signal; and (b) performing bi-linear interpolation on the pre-filtered signal, according to a predetermined aspect ratio, to output a format-converted signal.